This invention relates generally to injection molding and more particularly to a method of making a heated injection molding nozzle with a tip insert.
As seen in the applicant""s U.S. Pat. Nos. 4,557,685 which issued Dec. 10, 1985 and 4,768,283 which issued Sep. 6, 1988, injection molding nozzles having a tip aligned with the gate to provide hot tip molding are well known. Apparatus having a hot tip provided by a torpedo seated in the front end of a nozzle is also known. For instance, the applicant""s Canadian Patent Application Number 2,082,700 which was laid open May 13, 1994 shows a torpedo having a tip held in place by a nozzle seal which slides into a seat in the front end of the nozzle. U.S. Pat. No. 5,658,604 to Gellert et al. which issued Aug. 19, 1997 similarly shows a torpedo with a tip which is held in place by a nozzle seal which is screwed into a seat in the front end of the nozzle. As seen in the applicant""s U.S. Pat. No. 5,494,433 which issued Feb. 27, 1996, it is also known to have the tip provided by a side gate seal which screws into the nozzle.
As seen in U.S. Pat. No. 5,704,113 to Mold-Masters which issued Jan. 6, 1998, a method of making a nozzle wherein an inner portion, an outer collar portion and an electrical heating element are integrally brazed together is also known. The applicant""s U.S. Pat. No. 5,437,093 which issued Aug. 1, 1995, shows a method wherein an injection molding nozzle is made by first brazing an inner core, an outer collar portion and an outer sleeve together by heating to a temperature above a first melting temperature and then casting an electrical heating element into the space between them by heating to a temperature above a second lower melting temperature.
The previous apparatus and methods have the disadvantage that the portion providing the tip is either screwed or pressure fitted into place and therefore does not provide optimal heat transfer.
Accordingly, it is an object of the present invention to at least partially overcome the disadvantages of the prior art by providing a method of making an integral injection molding heating nozzle by integrally brazing a tip insert into a seat in the front end of the inner portion of the nozzle.
To this end, in one of its aspects, the invention provides a method of making an integral heated injection molding nozzle comprising the following steps. Making an elongated inner portion having a rear end, a front end, a melt bore extending therethrough from the rear end to the front end, and a general cylindrical outer surface with a spiral groove extending therearound. Making an outer collar portion to fit around the inner portion adjacent the rear end of the inner portion, the outer collar portion having a radial opening therethrough. Winding an electrical heating element into the spiral groove extending around the outer surface of the inner portion and mounting the outer collar portion in place around the inner portion with a terminal portion of the heating element extending outwardly through the radial opening through the outer collar portion. Closing in the radial opening around the at least one terminal portion. Applying a first brazing material having a predetermined melting temperature between the inner portion and the surrounding outer collar portion. Integrally brazing the inner portion, the outer collar portion, and the electrical heating element together by heating them in a substantially oxygen free atmosphere in a vacuum furnace to a temperature above the melting temperature of the first brazing material. Machining the integral nozzle to provide a desired outer shape and finish. Making a seat extending around the melt bore at the front end of the inner portion of the nozzle. Making a tip insert having a rear end, a rear portion extending forwardly from the rear end, a tip portion extending forwardly from the rear portion, and a melt bore extending forwardly therethrough from the rear end. The rear portion is made to fit in the seat at the front end of the inner portion of the nozzle with the melt bore through the tip insert extending from the melt bore through the inner portion of the nozzle. Inserting the tip insert into the matching seat at the front end of the inner portion of the nozzle. Then applying a second brazing material where the tip insert and the inner portion of the nozzle join, the second brazing material having a predetermined melting temperature substantially lower than the melting temperature of the first brazing material. Finally, integrally brazing the tip insert in place in the inner portion by heating them to a temperature above the melting temperature of the second brazing material and below the melting temperature of the first brazing material.